10 stocks hard at work during summer vacation

September is historically one of the worst performing months for the stock market. CNBC's Dominic Chu runs through the stats.

While many traders and investors took the summer months to get away and get in some rest and relaxation, the stock market was still hard at work.

During the span between Memorial Day (May 26) and Labor Day (Sept. 1), the large-cap S&P 500 index rose by more than 5 percent and set fresh record highs. That means that those who "sold in May and went away" missed out on a decent summer stock rally.

However, some stocks were harder at work than others, with many staging rallies of more than 20 percent.

Among the S&P 500 stocks that notched the strongest performances were names like Petsmart, which gained 29 percent during the summer season. Shares were helped along by a regulatory disclosure that activist hedge fund Jana Partners became the pet supply retailer's largest shareholder, with a near 10 percent stake. Jana Partners wants to explore ways to extract more value from the company.

Another star performer continues to be semiconductor giant Intel. Shares rallied more than 30 percent during summer vacation. A good chunk of those gains came on the heels of a bullish second-quarter earnings report that sent shares soaring by 9 percent on July 15. The company also increased its stock buyback authorization by $20 billion.

As for the single best-performing S&P 500 stock during the summer season, that distinction goes to a company that's gained 41 percent during that time frame. More recently the company has been making waves in its attempts to sign NBA all-star Kevin Durant to a mega endorsement deal, but ultimately losing out to larger rival Nike.

Under Armour stock has been a summer sizzler, but not just because of the share price appreciation. The company also signed super model Giselle Bundchen to an endorsement deal to help it sell products catered to women.

The top 10 best-performing S&P 500 stocks between Memorial Day and Labor Day this year are listed below.

On the downside, a number of companies on the index posted stock declines of 10 percent or more during that same time period.

Among some of the worst-performing stocks were higher-end retailers like Coach and Michael Kors, as well as other stocks in the consumer discretionary sector, includingMattel and Harley Davidson.

The single worst-performing stock in the index during the summer was Genworth Financial. The insurance company fell sharply after reporting earnings in July, amid investor concerns over whether the company had adequately planned for the costs associated with long-term care policies that help cover things like nursing homes and elderly care. Shares of Genworth dropped by 18 percent between Memorial Day and Labor Day this year.

The worst-performing stocks in the S&P 500 during this past summer are listed below.

Memorial Day to Labor Day Worst S&P Performers

Ticker

Company

% Chg.

GNW

Genworth Financial, Inc. Class A

-17.9%

KORS

Michael Kors Holdings Ltd

-16.9%

WAG

Walgreen Co.

-13.3%

DO

Diamond Offshore Drilling, Inc.

-12.9%

FMC

FMC Corporation

-12.7%

RRC

Range Resources Corporation

-11.4%

MSI

Motorola Solutions, Inc.

-11.3%

COH

Coach, Inc.

-11.3%

PVH

PVH Corp.

-11.2%

MAT

Mattel, Inc.

-10.6%

HOG

Harley-Davidson, Inc.

-10.1%

EXPD

Expeditors International of Washington, Inc.

-10.0%

Source: CNBC Analytics

As investors return from their vacations, and get back to work for the final four months of the year, the above stocks will garner added attention as investors try to ascertain whether that positive or negative momentum will continue. Others may look at some of the laggards for signs that turnarounds could be in the making.